No reason to use @admin in a button if UAC is disabled system-wide, although it should also be harmless. Leave it in if it's needed and UAC is enabled now, though.
From the new screenshot, it looks like you're running the whole process elevated, which is a bad idea, outside of special, temporary situations:
If UAC is on now, then Opus should not be elevated.
If UAC is off again, then the @admin code doesn't make much sense. But it's possible it is/was involved in what's happening.
I would like to rule out those two things. Whatever is causing the freeze may be a bug, but we have to work out which detail is triggering it to be able to fix it, if so.
Another thing I just noticed is that @admin is on the same line as the command. The command should be on a separate line:
@admin
"C:\Program Files (x86)\robocopy.exe" "C:\Struct" "{Rs|Please enter the path.\nThen click OK.|Y:\Models\}" /E /ZB /MON:50 /MOT:60 /MIR
If you want to send us a manually generated crash dump made while the freeze is happening, we may be able to look at that and locate the cause.